The present invention relates to an interface unit between a numerical controller and an electric power control circuit.
A numerical controller NC and a machine tool.TM. are usually interconnected via an electric power control circuit, commonly referred to as a PC.
FIG. 1 illustrates the general arrangement of a conventional numerically controlled machine tool. Reference numeral 1 indicates a microcomputer for numerical control, 2 its bus, 3 a tape reader for converting information punched in a command tape 4 into an electric signal, 5 a manual data input device (MDI) provided with numeric keys and character keys 6, a CRT for displaying the contents of an NC command program or the like, 7 a ROM for storing a system program or the like, 8 a RAM for operations, 9 a nonvolatile memory for storing the NC command program or the like (e.g., a magnetic bubble memory), 10 to 12 X-, Y- and Z-axis control circuits for driving X- , Y- and Z-axis motors 40 to 42 provided in the machine tool, 13 a buffer, 14 a driver and 15 a receiver. They constitute the numerical controller (NC). Reference numeral 20 designates a microcomputer for electric power control, 21 its bus, 22 a ROM for storing a control program or the like, 23 a RAM for operations, 24 a nonvolatile memory, for example, a magnetic bubble memory, 25 a buffer, 26 a receiver, 27 a driver, 28 a buffer, 29 a receiver and 30 a driver. They make up the electric power control circuit (PC). The numerical controller NC and the electric power control circuit PC are interconnected via the drivers 14 and 27 and the receivers 15 and 16. Data such as a motor start signal, a tool exchange command signal, a tool number and so forth, is delivered from the numerical controller NC to the electric power control circuit PC via the driver 14 and the receiver 26. The electric power control circuit PC responds to the input data to execute predetermined sequence control or the like, causing the machine tool TM to perform starting of the motors, a tool exchange or the like via the driver 30. Information such as the end of the tool exchange or the like is provided from the electric power control circuit PC to the numerical controller via the buffer 25, the driver 27, the receiver 15 and the buffer 13. After recognizing the information, the numerical controller NC performs the next process or the like.
Incidentally, it is sometimes desired to automatically control the actual speed (the cutter speed) from the side of the machine tool in accordance with, for example, a load on the machine tool during cutting, or the amount of cutting chip, so as to achieve higher precision or the like. With the conventional numerically controlled machine tool, however, the actual speed is determined by a speed command value in the NC command program and the override ratio. For changing the actual speed, there is no method but to modify the speed command in the NC command program or to manually change the override ratio, so that it is difficult to effect the above-mentioned control.